Various production processes are typically used under high-temperature conditions in numerous chemical industrial fields. Measures to prevent leakage of liquids and gases are employed in the line couplings and so on of these production lines using, for example, packings and welding. Packings have superior flexibility, for example, were previously made from organic polymer materials. However, the maximum heat resistance of these organic polymer materials was the 350° C. achieved when using liquid crystal polyester, and at temperatures there above, it was necessary to use metal packings. These metal packings, however, had the problem of having inferior flexibility as compared with organic polymer materials. Although aluminum foil or aluminum-deposited film has superior gas impermeability, it is not transparent. In addition, since aluminum foil is a metal, it cannot be used as a sealing material wrapped around threaded portions. In addition, although there are silica-deposited films that are transparent and have superior gas impermeability, since the base material of these silica-deposited films is an organic compound film, it similarly cannot be used under high-temperature conditions above 350° C. In addition to being used as packings, these gas-impermeable materials may also be used by being wrapped around joint threads, wrapped around tubes or affixed to flat members. On the other hand, sheets using clay minerals in the form of mica or vermiculite and the like are used as gland packings used under high-temperature conditions (Japanese Patent Application Laid-Open No. H6-95290, Japanese Patent Application Laid-Open No. H5-254824, Japanese Patent Application Laid-Open No. 2002-30255, Japanese Patent Application Laid-Open No. S50-2699). However, since these sheets cannot be made to be completely free of cracks and pinholes, packings and gaskets fabricated from these sheets have the problem of being unable to completely seal gases.
Clay is known to form a film having an aligned particle orientation by dispersing in water or alcohol, spreading the dispersion onto a glass sheet and allowing to dry by standing undisturbed. For example, azimuth-oriented samples for X-ray analysis have been prepared using this method (Haruo Shiramizu, “Clay Mineralogy (Nendo Kobutsu Gaku)—Basics of Clay Science”, Asakura Shoten, p. 57 (1988)). However, in the case of forming a film on a glass sheet, it was difficult to peel the clay film from the glass sheet, cracks formed in the film when peeling from the glass sheet and other problems occurred that made it difficult to obtain a self-supporting film. In addition, even if the film was able to be peeled from the glass sheet, the resulting film was brittle and lacked sufficient strength.
Clay thin films have recently been produced by applying the Langmuir-Blodgett method (Yasushi Umemura, Clay Science, Vol. 42, No. 4, p. 218-222 (2003)). In this method, however, since a clay thin film is formed on the surface of a substrate made from a material such as glass, it was not possible to obtain a clay thin film having the strength of a self-supporting film. Moreover, various methods for preparing, for example, functional clay thin films and the like have been reported in the past. Examples of these methods include a method for producing a clay thin film comprising forming an aqueous dispersion of a hydrotalcite-based interlayer compound into a film followed by drying (Japanese Patent Application Laid-open No. S53-39318), a method for producing a layered clay mineral thin film in which the binding structure-possessed by the layered clay mineral is fixed by carrying out heat treatment that promotes a reaction between the layered clay mineral and phosphoric acid or a phosphate group (Japanese Patent Application Laid-open No. S55-142539), and an aqueous composition for film treatment comprising a smectite-based clay mineral and a metal complex compound having a valence of two or more (Japanese Patent Application Laid-open No. H5-262514), and numerous examples of these methods exist. However, a clay film having mechanical strength enabling use as a self-supporting film and superior flexibility has yet to be developed.
In general, clay, and particularly clay having superior plasticity, is easily dispersed in water and can be easily made into a uniform film. In addition, such clay also facilitates the production of complexes due to its superior affinity with hydrophilic chemical substances. Clay offering such advantages conversely has inferior moisture resistance, and if immersed in water, swells and becomes brittle until it finally is unable to maintain its form. Fabrics made from various fibers, such as plain-woven fabrics and non-woven fabrics, are available commercially, and these fabrics are characterized by having adequate mechanical strength, flexibility and durability with respect to repeated bending. The heat resistance and chemical resistance of these fabrics are dependent on the fiber raw materials that compose the fabric. Examples of fibers that compose these fabrics include mineral fibers, glass wool, ceramic fibers, metal fibers, ceramic fibers, plant fibers and organic polymer fibers. However, since these fabrics are unable to completely seal the spaces between fibers, they have the problem of lacking gas impermeability. In the case of practical use of clay films, the clay film is used to as to be in contact with a member made of another type of material in many cases. At this time, fixation, joining and so forth between the clay film and member made from another type of material is required to be able to be carried out easily, uniformly and reliably. In the case of adhering two clay films, it is possible to use an adhesive having high adhesive strength with a clay film. In addition, in the case of adhering a clay film with another type of material such as metal, glass, paper, plastic or rubber, it is possible to use an adhesive capable of adhering both the clay film and the other type of material. These adhesives can be acquired comparatively easily, and clay films or clay films and other types of materials can be adhered by these adhesives. However, the uniform coating of these adhesives onto a clay film followed by the uniform and reliable adhesion thereto has previously been unsuccessful. In the case of adhesives using polar solvents in particular, there is the problem of the clay film being susceptible to swelling. In addition, since a clay film itself has high gas impermeability, considerable time is required for drying and it was difficult to produce a thick film.